Question

1. Light first travels through air (n = 1.00) and then impinges an oil drop (n = 1.20) that is floating on a layer of water (n = 1.33) that sits on glass (n = 1.50). List every surface boundary where a 180° phase shift would be observed for reflected light.

2. Which of the following must be the same for two rays of light to be considered to be coherent? Choose all that apply from the following: (a) frequency, (b) wavelength, (c) wave speed, (d) wave phase and (e) wave amplitude.

Answer 1

1) If light is reflected from higher refractive index medium than the one in which it is travelling then there is a phase shift of 180 degrees .

The light reflected from the oil surface will have a phase shift of 180 degree . Similarly light reflected from water will also show a phase shift of 180 degree . So will the light reflected from the surface of glass also . Hence a phase shift of 180 degree will be observed from all the surfaces of the boundary since the ray is travelling from lighter to a optically denser medium in all the cases.  

2)two coherent sources should have same frequency and wave phase